Disposable absorbent products have been known for some time, including such products as disposable diapers, sanitary napkins, wound dressings, bandages, incontinent pads, and the like. These products incorporate an absorbent batt which is used to absorb and hold or contain body fluids. Initially, in many of these products, especially diapers and sanitary napkins, the absorbent batt comprised what is termed "wadding" or plies of tissue. The wadding was disposed between an impermeable backing and a permeable facing and the plies of tissue were used to absorb and, hopefully contain the liquid within the product. A diaper which utilizes such an absorbent batt is disclosed in U.S. Reissue Pat. No. 26, 151.
The wadding type of batt was replaced, for the most part, by an improved absorbent batt which comprises what is termed "fluffed wood pulp fibers". This absorbent batt comprises a layer of individualized wood pulp fibers with the layer having substantial thickness. A diaper which incorporates such a fluffed wood pulp absorbent batt is described in U.S. Pat. No. 2,788,003. This diaper had improved absorbent capacity and somewhat better containment than a diaper using a wadding layer. Also the fluffed wood pulp layer is quite soft, flexible and conformable and hence, produces an improved diaper over diapers using wadding as the absorbent layer.
Though the fluffed wood pulp absorbent batts have improved capacity, the total absorbent capacity of the batts is often not entirely used, causing leakage and/or staining. Because fluid to be absorbed is generally deposited in a localized area within the absorbent batt and radiates equally in all directions, the fluid tends to reach the longitudinal sides of a generally-rectangular batt before it reaches the ends of the batt. Consequently, the absorbent product may leak at the longitudinal sides.
The ability of a densified pulp to transport fluid more effectively than traditional products made from a uniform wood pulp fluff has been recognized. A. Burgeni and C. Kapur, "Capillary Sorption Equilibria in Fiber Masses," Test Res. J., Vol. 37:5, p.356, (1976).
A multi-layer diaper is disclosed in Mesek et al. U.S. Pat. No. 3,768,480. Mesek et al. describes a batt having a density gradient achieved by gradually decreasing the proportion of long fibers and increasing the level of short fibers in a blend. Typically, this structure is then bonded with a latex binder and serves as a facing layer in conjunction with a second batt layer and a water impervious backing sheet.
U.S. Pat. No. 3,771,525 discloses a traditional layered structure. A high density cotton core is wrapped with a low density, loose cotton fiber layer.
A method of making a selectively densified fiber batt obtained from an embossed pattern made permanent by employing an adhesive is described in U.S. Pat. No. 4,134,948. This method makes an absorbent fabric comprising a batt of randomly arranged, intermingled cellulosic fibers having a plurality of high loft, loosely compacted regions separated from each other by highly compressed regions. These compressed regions are formed by moistening the batt, embossing the batt for providing a pattern in the surface, and applying an adhesive material to the patterned surface. The adhesive penetrates through the compressed regions to form banded fiber networks and only partially penetrates through the high loft absorbent regions.
In U.S. Pat. No. 4,540,454, a method of forming a relatively thin absorbent product is disclosed. The product has at least two layers. One layer may be superimposed on the other by air layering. The layers are then compressed at a pressure adequate to collapse the entire structure which promotes intimate contact between the layers; a wicking layer and an absorbing layer. The structure in its compressed form is less than one-half its thickness in the uncompressed form. The absorbing layer is a low density, resilient, fibrous web consisting of randomly disposed, frictionally entangled fibers which result in a web having a dry bulk recovery of at least 60 percent, an initial dry bulk of at least 20 cc/gm and a weight less than about 2 oz/yd.sup.2. The fibrous web making up the absorbing layer is used to specially distribute superabsorbent material so that upon exposure to an aqueous, swelling occurs with minimal interference from adjacent superabsorbing material. The transporting or wicking layer is a high density structure made of particles such as cellulosic fibers, peat moss, or mixtures thereof.